Conventional current sensors for detecting AC components in a DC circuit operate on the principle of detecting an AC voltage induced in an inductive component via a time-varying field generated by the AC component, wherein the induced AC voltage corresponds to the AC component to be measured, in particular is proportional to it. So-called current converters are, in particular, used as inductive components, which are made up of coils having a magnetic core material and which achieve high inductance values while at the same time having a compact design and a low number of turns.
In particular in DC circuits of photovoltaic systems, DC current strengths in the order of several amperes up to several dozen amperes frequently occur. At the same time, the amplitudes of AC components which, for example, are generated by arcs to be detected in the DC circuit in the frequency range of several kHz up to several hundred kHz, are only a few milliamperes.
When using current sensors having a magnetic core material, a saturation of the core material must be avoided, in particular in the case of such high DC current strengths. For this purpose, either a core material having a low permeability is used or the volume of the core is increased. However, a lower permeability has a negative effect on the sensitivity and linearity of the sensor, which becomes noticeable in particular when measuring very small AC currents across a wide frequency range. A larger core volume in turn has a negative effect on the size and thus the costs.
Alternatively, current sensors are known which are configured as an air coil without a magnetic core and which are arranged toroidally around a conductor in which the AC component is to be measured. Due to the lack of core material, they are free of saturation effects and are thus well suited for the measurement of AC components on high DC currents. Such so-called Rogowski sensors are in particular suited for the measurement of AC components having large amplitudes or for the measurement of small AC components at high frequencies. However, they are only somewhat suitable for the measurement of small AC components at low frequencies.
The sensitivity of inductive current sensors is frequency-dependent, so that the lower the frequency of the AC component to be measured is, the higher the provided inductance must be. The inductance may be increased via an increase in the permeability of the core material or via a greater number of turns, thus resulting in increased size and costs.